1. Field of Invention
The present invention relates generally to data communications, and to a method and apparatus for identification of radar signals that may need to be avoided by the wireless system.
2. Discussion of Background
Wireless Local Area Network (WLAN) devices must coexist with radar in the 5 GHz frequency bands. Interference mitigation techniques are required to enable WLAN devices to share these frequency bands with radar systems. The general requirement is that the WLAN devices detect interference, identify the radar interfering sources, and avoid using the frequencies used by the radar. Dynamic Frequency Selection (DFS) is used as a spectrum sharing mechanism by certain standards committees that define rules dictating the use of the 5 GHz space. For example, the European Telecommunications Standards Institute (ETSI), which is involved in developing standards for Broadband Radio Access Networks (BRAN), requires that transceiver equipment for use in HIPERLAN (High Performance Radio Local Area Networks) employ DFS mechanisms to detect interference from other systems, notably radar systems. One goal is to provide a uniform spread of equipment loading across a number of channels, such as fourteen channels of 330 MHz each, or 255 MHz each for equipment used in bands 5470 MHz to 5725 MHz.
Present proposals from the ETSI BRAN committee provide various guidelines for radar detection. These include detecting and avoiding radar signals that only appear at a level above a certain pre-defined threshold, such as −62 dBm. In one implementation, detection is based on a simple algorithm to see whether there are any instances of signals above the −62 dBm threshold during a ten second startup listening period. Another proposed guideline is that detection during normal operation should be addressed by periodically suspending all network traffic and listening in startup mode for any instances of signals above the −62 dBm threshold level.
Along with guidelines proposed by the present standards committees, the radar and satellite industries increasingly expect 5 GHz WLAN devices to detect and avoid radar signals during normal operation.
However, the present proposed methods of radar detection and avoidance are generally insufficient, especially in view of increased network traffic in the 5 GHz radio spectrum and the need for increased bandwidth among WLAN devices. The WLAN devices will need to quickly detect and avoid radar that have, among others, critical military, meteorological, and navigational functions. Therefore, additional detection and avoidance techniques are needed.
However, regardless of the techniques utilized, an important aspect of any system is the ability to detect and distinguish radar signals from other traffic or interference that may also be present in the spectrum of the wireless device.